The present invention relates to a flexible, high dielectric constant polyimide film, composite and high dielectric constant polyimide liquid for use in electronic circuitry and electronic components including multilayer printed circuits, flexible circuits, semiconductor packaging and buried film capacitors.
Conventional decoupling capacitors are mounted on the surface of printed circuits boards and are connected to the power and ground planes near the integrated circuit. For a typical printed circuit board having a large number of integrated circuits, a corresponding large number of decoupling capacitors is typically required to provide for current requirements and to reduce system noise. Such capacitors, however, have disadvantages since they occupy considerable printed circuit board surface space, increase the number of solder joints and, therefore, reduce the system reliability.
Recently, a new capacitor design, called a buried film capacitor, has been developed which generates sufficient bypass capacitance to be shared throughout the printed circuit board. For example, U.S. Pat. No. 5,162,977, issued to Paurus et al on Nov. 10, 1992, discloses a printed circuit board which includes an embedded high capacitance power distribution core consisting of a signal ground plane and a power plane separated by a dielectric core element having a high dielectric constant. This buried capacitive structure not only provides electromagnetic interference (EMI) suppression but also makes it possible to remove up to 98% of the discrete bypass capacitors from the printed circuit board. The dielectric core element disclosed in U.S. Pat. No. 5,162,977 consists of glass cloth impregnated with an epoxy resin loaded with a ferroelectric ceramic powder having a high dielectric constant. Such conventional glass fiber impregnated epoxy resin systems, however, provide a capacitance density of up to 2000 picofarads/inch.sup.2, which is not sufficient for the inrush current requirements of most integrated circuits.
The present invention provides a flexible, high dielectric constant polyimide in the form of a film, composite or liquid, which when used as the dielectric core component of an embedded high capacitance power distribution core in a printed circuit board or in semiconductor packaging, provides a much higher capacitance surface density of 200,000 picofarads/inch.sup.2 due to the higher dielectric constants obtainable and the thinner film structures employed. A printed circuit board with such capacitance characteristics typically requires no additional decoupling for the associated printed circuit board components, and thus obviates the need for decoupling capacitors which are mounted externally on the printed circuit board.